Severe gastroenteritis in both developed and less developed countries is caused by rotaviruses and currently there is only one licensed vaccine available. Disease aspect of rotavirus results from rapid replication of the virus in i ntestinal cells, outstripping the ability of the intestine to replace damaged cells. The virus is a 70 nm non-enveloped virus containing 11 segments of double stranded RNA genome. To date three structural proteins (VP3, VP4 and VP7) and two non-structural proteins (NSP2 and NSP4) have been shown to be associated with pathogenicity and one nonstructural protein, NSP1 was shown to be associated with host range. The NSP4 is associated with diarrhea and cytotoxicity. Progress:1. Lab-based regulatory research Lab was set-up to perform rotavirus potency testing; Rotavirus plaque-assay for potency testing was developed. Several vaccine lots have been released based on in-house potency testing and by review of submitted lot release protocols. This is an on-going CBER mission-related activity. 2. Mission-oriented research. We have produced novel mutant forms of human rotavirus NSP4 that have potential in using as toxoid vaccines. Studies are underway to fully characterize the mutants.